JP2002325759A - Computed tomograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a computed tomograph capable of improving time resolution. SOLUTION: This device is provided with a setting means for setting a concerned area in a prescribed image displayed on a display device 7 and an image reconstituting means 5 for finding first image data by applying convolutional operation to projection data used for reconstituting the prescribed image and applying back projection operation to data inside the concerned area, finding a difference between projection data for prescribed images and timewisely adjacent projection data and obtaining a second image timewisely deviated from the first image by applying the convolutional operation to these differencial data and applying the back projection operation while overlapping the data on the first image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer tomography apparatus for obtaining a tomographic image of a specific part of a subject.

[0002]

2. Description of the Related Art In a computed tomography apparatus, an X-ray source and a detector are opposed to each other with a subject interposed therebetween, and the X-ray source and the detector are rotated by a predetermined angle around the subject by a predetermined angle.
The line is scanned with respect to the subject, and the output signal of the detector at this time is collected as projection data for each angle. Then, these projection data are image-reconstructed by a convolution / back-projection calculation to obtain a tomographic image of the subject.

Incidentally, such a device is disclosed in Japanese Patent Publication No. 1-23.
As described in Japanese Patent Publication No. 136, there is a technique for obtaining and displaying many tomographic images in a short time. According to this technique, M pieces of projection data that are continuous over one rotation (360 degrees) of an X-ray source with respect to a subject are collected.

Next, the first 360-degree projection data (first
Projection data to m-th projection data), perform a convolution operation, perform a back projection operation to reconstruct an image,
First image data (tomographic image) is obtained and displayed.

Next, a difference between the (m + 1) th projection data and the first projection data is obtained, a convolution operation is performed on the difference data, and a back projection operation is performed on the first image data. Thus, the second image data is obtained and displayed.

Thereafter, each image data shifted by one projection data is sequentially obtained and displayed. Therefore, by continuously displaying these image data, a temporally continuous dynamic image is displayed.

[0007]

However, in recent apparatuses, the time resolution is not sufficient because the speed of X-ray scanning is increased and the number of projection data is increased. Therefore, an object of the present invention is to provide a computed tomography apparatus capable of improving the time resolution.

[0008]

In order to achieve the above object, the present invention is to continuously scan a subject with radiation for at least one rotation to obtain each projection data, and reconstruct these projection data into an image. In a computed tomography apparatus for obtaining a tomographic image of the subject, a display means for displaying a predetermined image reconstructed based on the projection data, and a region of interest in the predetermined image displayed on the display means. Setting means for setting, performing a convolution operation on the projection data used to reconstruct the predetermined image, and performing a back projection operation on data in the region of interest to obtain first image data At the same time, the difference between the projection data for the predetermined image and the projection data adjacent in time is obtained, and the difference data is subjected to a convolution operation, Serial is characterized in that anda image obtaining means for obtaining a second image shifted in time with the first image by back projection operation to overlap the first image data.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a computer tomography apparatus. The X-ray source 2 and the detector 3 are arranged to face each other with the subject 1 interposed therebetween. The X-ray source 2 is a fan beam X
The detector 3 has a configuration in which a plurality of X-ray detection elements are arranged, and is connected to the data collection unit 4.

The data collecting section 4 has a function of collecting and storing output signals of the detector 3 as projection data. In this case, the X-ray source 2 and the detector 3 are connected to the object 3 as shown in FIG. Projection data P1, P when 300 scans are continuously performed at a rotation angle of 360 degrees or more with respect to 1
2,... P300, P301... Are sequentially arranged and stored. Further, the image reconstruction unit 5 has a function of performing a convolution operation and a back projection operation on the projection data. The computer 8 performs overall control. Further, the computer 8 receives an input from a console (not shown). Further, an image memory 6 and a display device 7 are provided. Next, the operation of the apparatus configured as described above will be described with reference to the flowchart shown in FIG.

The X-ray source 2 emits a fan beam X-ray. This X-ray passes through the subject 1 and reaches the detector 3. The detector 3 outputs an electric signal corresponding to the X-ray dose input by each X-ray detection element. In this case, X-rays are emitted for each rotation angle of one rotation (360 degrees / 300 projections) with respect to the subject 1.

In step s1, the data collection unit 4
An output signal of the detector 3 input at every predetermined angle is collected as projection data, and for example, as shown in FIG.
(60 degrees / 300 projections), each projection data P1, P2, ...
P300, P301..., PM are sequentially arranged and stored.

Next, in step s2, the image reconstruction unit 5
Reads out the projection data P1 to P300 from the data collection unit 4 and reconstructs an image of the projection data P1 to P300 by a convolution / back-projection operation to obtain first image data. The first image data is temporarily stored in the image memory 6. It is sent to the display device 7 and displayed.

Next, in step s3, m is set to "1", in the next step s4, the interval i of the projection data for displaying an image is set to "0", and in the next step s5, m = m +
1 (= 2) is set.

Next, in step s6, the image reconstruction unit 5
Reads the projection data P301 and P1 from the projection data stored in the data collection unit 4, finds difference data between the projection data P301 and P1, and sets the difference data as the second sub-projection data. That is, m-th sub-projection data = (m + 299-th projection data) − (m−1-th projection data) is obtained.

Next, at step s7, the image reconstruction unit 5
Calculates the convolution of the m-th sub-projection data,
Next, the result of this convolution operation is referred to as (m-1)
The m-th image data is obtained by performing a back-projection operation on the image data.

Next, in step s8, the image reconstruction unit 5
Is i = i + 1, and in the next step s9, it is determined whether i is smaller than n. As a result of this determination, if i is smaller than n, the image reconstruction unit 5 sequentially obtains each image data shifted by one projection data.

On the other hand, if i is larger than n, the m-th image data is sent to the display device 10 in the next step s11. Thus, the image of the m-th image data is displayed on the display device 10. As a result, the image data obtained every n projection data is sent to the display device 10 and displayed.

As described above, according to the first embodiment, even if the number of projection data increases, by displaying image data obtained for every n projection data, a continuous dynamic image for every n projection data can be obtained. Can be projected. Next, a second embodiment of the present invention will be described with reference to a tomographic image calculation flowchart shown in FIG.

In step s1, the data collection unit 4 sets each projection data P1, P2,... P300, P301.
M are sequentially arranged and stored, and in the next step s2, the image reconstructing unit 5 reconstructs the image of each of the projection data P1 to P300 by a convolution / back-projection operation to obtain first image data. Remember. The first image data is sent to the display device 7 and displayed.

Next, in step s3, the image reconstruction unit 5
Sets m to “1” and sets i to “0” in the next step s4
Is set to “0” in the sub-image memory (not shown) in the next step f1. Then, the image reconstruction unit 5 sets i = i + 1 in step s5.

Next, in step s6, the image reconstruction unit 5
Are the (m + i + 2999) th projection data and the (m + i-
1) Difference data from projection data is obtained, and this difference data is used as i-th sub-projection data. Next, in step f2, the image reconstruction unit 5 obtains second image data by performing a convolution / back-projection operation on the i-th sub-projection data. Next, in step s9, it is determined whether i is smaller than n. If it is determined that i is smaller than n, the process returns to step S5.

On the other hand, if i is greater than n, the image reconstructing unit 5 proceeds to step f4 and adds the sixth image data to the m-th image data, and outputs the image data obtained by the addition to the display device 10. send. As a result, new image data added for every n projection data is obtained, and this image data is displayed on the display device 10. As described above, according to the second embodiment, it goes without saying that the same effects as in the first embodiment can be obtained. Next, a third embodiment of the present invention will be described with reference to the flowchart shown in FIG.

In step s1, the data collection unit 4 sets each of the projection data P1, P2,... P300, P301.
M are sequentially arranged and stored. In the next step s2, first image data is obtained, and in the next step s3, m is set to "1".

Next, in step m1, the direction of time n is specified. In this case, n indicates each projection data in the temporally forward direction by n projections if -n is specified,
If + n is specified, it indicates each projection data in the backward direction in time by n projections.

Thereafter, n is determined in step m2,
If n is “+”, then in the next step m3, m + n ≦
It is determined whether or not M, and if m + n ≦ M is no, n = M
Set -m. In the next step m5, m = m + 1 is set. Here, M is the number of projection data.

Next, in step s6, the image reconstruction unit 5
Calculates difference data between the (m + 299) th projection data and the (m-1) th projection data, and uses the difference data as the mth sub-projection data.

Next, in step s7, the image reconstruction unit 5
Calculates the convolution of the m-th sub-projection data,
The m-th image data is obtained by performing a back-projection operation on the (m-1) -th image data.

Next, in step s8, i = i + 1 is set, and in the next step s9, it is determined whether i is smaller than n. If it is determined that i is smaller than n, the process returns to step m5. On the other hand, if i is larger than n, the image reconstruction unit 5 sends the m-th image data to the display device 10.
Thus, the image of the m-th image data is displayed on the display device 10.

On the other hand, if n is "-" in step m2, the absolute value of n is obtained in step m7, and the image reconstruction unit 5 determines in step m8 whether mn> 0. If no, n = m-1 is set in step m9. Next, m = n-1 is set in step m10.

Next, in step s6, the image reconstruction unit 5
Calculates difference data between the m-th projection data and the (m + 300) -th projection data, and uses the difference data as the m-th sub-projection data. That is, m-th sub-projection data = (m-th projection data)-(m-th + 300 projection data) is obtained.

Next, in step s7, the image reconstruction unit 5
Calculates the convolution of the m-th sub-projection data,
Next, the result of the convolution operation is superimposed on the (m + 1) th image data, and the backprojection operation is performed to obtain the mth image data.

Next, in step s8, the image reconstruction unit 5
Is i = i + 1, and in the next step s9, it is determined whether i is smaller than n. If it is determined that i is smaller than n, the process returns to step m10. On the other hand, if i is greater than n, the m-th image data is sent to the display device 10.
Thus, the image of the m-th image data is displayed on the display device 10.

As described above, in the third embodiment, the temporal front-back direction of the image is specified. Therefore, when an image at a certain time is displayed from the collected projection data, the image is displayed. Using projection data acquired later or earlier than the projection data used for
By subtracting the difference from the projection data constituting the image at a certain time, images that are later and earlier in time than the image at a certain time can be continuously displayed on the display device 10. Next, a fourth embodiment of the present invention will be described. This embodiment is a modification of the third embodiment, and the setting of n is designated by a mouse or a pointer such as a trackball. The processing flow will be described with reference to the flowchart shown in FIG. After collecting each projection data in step s1, first image data is obtained in step s2, and m = 1 is set in step s3.

Next, in step k1, the state of the pointer is read, and in the next step k2, the state of the pointer read this time is compared with the state of the pointer read last time. As a result of this comparison, if there is a change, step k4
Is set to n. In this case, n sets the temporal direction and the number of projections according to the change amount of the pointer. Thereafter, the process proceeds to step s4 shown in FIG. Next, a fifth embodiment of the present invention will be described.

In the first to fourth embodiments, the reconstructed image is displayed but is not stored in an image storage device such as a disk. This is because enormous storage memory capacity is required to store all images.
However, when a storage instruction is given to an image displayed according to the fourth embodiment, the image may be stored in the image storage device. Thus, only necessary image data can be stored. Next, a sixth embodiment of the present invention will be described.

In the fifth embodiment, the displayed image is stored as it is, but the image according to the present invention is an image using 360-degree projection data. On the other hand, there is known a half image reconstructing method in which an image is reconstructed by projection data of 180 ° + fan angle in order to further improve the time resolution.

Therefore, according to the present invention, the m-th image is displayed,
If a half image is designated at that time, the half image is reconstructed using the first projection data (m-th projection data) of the m-th image as the first projection data. It may be displayed. In that case, the half image may be stored in the image storage device as needed. In this way, only necessary half images can be stored. Next, a seventh embodiment of the present invention will be described with reference to the flowchart shown in FIG.

At step h 1, the m-th image data is displayed on the display device 10. In this state, in the next step h2, a region of interest 16 is set on the subject 2 in the image as shown in FIG.

Next, the image reconstructing section 5 sets mM = M-300 in step h3, and sets the number nn of time curve sampling in the next step h4. Note that the sampling number nn does not include “0”. Next, in step h5, n = mMm / nn is determined.

Next, at step h6, the image reconstruction unit 5
Reads the projection data P1 to P300 from the data collection unit 6, performs a convolution operation on the projection data P1 to P300, and then performs a back projection operation only on the pixels in the region of interest 16 to reconstruct an image. To obtain first image data. Next, in step h7, the image reconstructing unit 5 converts the region of interest 16
The average value of the pixel values in is obtained and stored. Then step h
From 8 to h10, m = 1, i = 0, and m = m + 1 are set.

Next, at step h11, the image reconstructing section 5 obtains difference data between the (m + 299) th projection data and the (m-1) th projection data, and uses this difference data as the mth sub-projection data. And

Next, in step h12, the image reconstructing unit 5 performs a convolution operation on the m-th sub-projection data, and applies only the (m−m)
1) The m-th image data is obtained by performing a back-projection operation on the image data.

Next, at step h13, i = i +
Set 1. Next, in step h14, i <n
Is determined, and if yes, the process returns to step h10. If no, in step h15, the average value of the pixel values in the region of interest 16 is obtained from the m-th image data and stored. Then, in step h16, it is determined whether the image is the last image. If the image is in the middle, the process returns to step h9. In the case of the last image, a time curve is created in step h17. According to the seventh embodiment, the time curve of the region of interest 16 can be obtained. Next, the eighth aspect of the present invention
An example will be described.

The half image may be reconstructed as follows based on the time curve created in the seventh embodiment. Further, a time curve having a higher time resolution may be obtained from these half images. The procedure will be described below. (A) A time curve is created and displayed according to the seventh embodiment.

(B) The operator designates the sampling time of the time curve while watching the time curve. The time can be specified arbitrarily, but the important part of the time curve is
It is desirable to specify coarsely small portions with little change. In this case, to make the specification as easy as possible,
Create a good human interface.

(C) Create a half image at the designated sampling time. In this case, the half image may reconstruct the entire photographing area or only the ROI portion. When the entire photographing area is reconstructed, the image is usually stored in the image storage device. (D) A time curve is created from the reconstructed half image and displayed.

[0049]

As described above, according to the present invention, a computed tomography apparatus with improved time resolution can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a computer tomography apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a collection direction of each projection data in the same device.

FIG. 3 is a flowchart of tomographic image calculation in the first embodiment of the apparatus.

FIG. 4 is a flowchart of tomographic image calculation in a second embodiment of the apparatus.

FIG. 5 is a flowchart of tomographic image calculation in a third embodiment of the apparatus.

FIG. 6 is a flowchart of tomographic image calculation in a fourth embodiment of the apparatus.

FIG. 7 is a flowchart of tomographic image calculation in a seventh embodiment of the apparatus.

FIG. 8 is a view showing a region of interest in the apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Subject, 2 ... X-ray source, 3 ... Detector, 4 ... Data acquisition part, 5 ... Image reconstruction part, 6 ... Image memory, 7 ...
Display device.

Claims (2)

[Claims] 1. A computed tomography apparatus for continuously scanning a subject with radiation for at least one rotation to obtain respective projection data, reconstructing the projection data into an image, and obtaining a tomographic image of the subject. Display means for displaying a predetermined image reconstructed based on the projection data; setting means for setting a region of interest in the predetermined image displayed on the display means; reconstructing the predetermined image A convolution operation is performed on the projection data used in the above, and a back projection operation is performed on the data in the region of interest to obtain first image data. A difference between adjacent projection data is obtained, a convolution operation is performed on the difference data, and a back projection is performed on the first image data. An image acquisition unit that obtains a second image temporally shifted from the first image by performing an arithmetic operation. 2. The computed tomography apparatus according to claim 1, further comprising a time curve creating unit that creates a time curve in the region of interest based on the image obtained by the image obtaining unit. .